pkg_install: modify log levels & print destdir by default. (#891)

After this change, log levels are defined by the following:
* -q: only print errors (not even warnings)
* (default): print errors, warnings, infos
* -v: print above & also debug logs.

There are no errors and warnings logs at this moment.
The existing verbose logs about file operations are
categorized as debug logs, so they are only printed
when -v is set.

By default (if no flag is set), the destdir is printed
as an INFO level log.

Also improve the logging format to be similar to bazel's output, e.g.

    INFO: Installing to /tmp/inst

Fixes #889

Co-authored-by: HONG Yifan <elsk@google.com>

pkg/private/install.py.tpl

diff --git a/pkg/private/install.py.tpl b/pkg/private/install.py.tpl
index 3a29f05..b6c276b 100644
--- a/pkg/private/install.py.tpl
+++ b/pkg/private/install.py.tpl
@@ -65,29 +65,29 @@
 
     def _chown_chmod(self, dest, mode, user, group):
         if mode:
-            logging.info("CHMOD %s %s", mode, dest)
+            logging.debug("CHMOD %s %s", mode, dest)
             os.chmod(dest, int(mode, 8))
         if user or group:
             # Ownership can only be changed by sufficiently
             # privileged users.
             # TODO(nacl): This does not support windows
             if hasattr(os, "getuid") and os.getuid() == 0:
-                logging.info("CHOWN %s:%s %s", user, group, dest)
+                logging.debug("CHOWN %s:%s %s", user, group, dest)
                 shutil.chown(dest, user, group)
 
     def _do_file_copy(self, src, dest):
-        logging.info("COPY %s <- %s", dest, src)
+        logging.debug("COPY %s <- %s", dest, src)
         shutil.copyfile(src, dest)
 
     def _do_mkdir(self, dirname, mode):
-        logging.info("MKDIR %s %s", mode, dirname)
+        logging.debug("MKDIR %s %s", mode, dirname)
         os.makedirs(dirname, int(mode, 8), exist_ok=True)
 
     def _do_symlink(self, target, link_name, mode, user, group):
         raise NotImplementedError("symlinking not yet supported")
 
     def _maybe_make_unowned_dir(self, path):
-        logging.info("MKDIR (unowned) %s", path)
+        logging.debug("MKDIR (unowned) %s", path)
         # TODO(nacl): consider default permissions here
         # TODO(nacl): consider default ownership here
         os.makedirs(path, 0o755, exist_ok=True)
@@ -107,7 +107,7 @@
         self._chown_chmod(dst, entry.mode, entry.user, entry.group)
 
     def _install_treeartifact(self, entry):
-        logging.info("COPYTREE %s <- %s/**", entry.dest, entry.src)
+        logging.debug("COPYTREE %s <- %s/**", entry.dest, entry.src)
         shutil.copytree(
             src=entry.src,
             dst=entry.dest,
@@ -147,9 +147,9 @@
 
     def _install_symlink(self, entry):
         raise NotImplementedError("symlinking not yet supported")
-        logging.info("SYMLINK %s <- %s", entry.dest, entry.link_to)
-        logging.info("CHMOD %s %s", entry.dest, entry.mode)
-        logging.info("CHOWN %s.%s %s", entry.dest, entry.user, entry.group)
+        logging.debug("SYMLINK %s <- %s", entry.dest, entry.link_to)
+        logging.debug("CHMOD %s %s", entry.dest, entry.mode)
+        logging.debug("CHOWN %s.%s %s", entry.dest, entry.user, entry.group)
 
     def include_manifest_path(self, path):
         with open(path, 'r') as fh:
@@ -170,6 +170,7 @@
             self.entries.append(entry)
 
     def do_the_thing(self):
+        logging.info("Installing to %s", self.destdir)
         for entry in self.entries:
             if entry.type == manifest.ENTRY_IS_FILE:
                 self._install_file(entry)
@@ -241,13 +242,14 @@
     loudness = args.verbose - args.quiet
 
     if args.quiet:
-        logging.getLogger().setLevel(logging.ERROR)
+        level = logging.ERROR
     elif loudness == 0:
-        logging.getLogger().setLevel(logging.WARNING)
-    elif loudness == 1:
-        logging.getLogger().setLevel(logging.INFO)
-    else:  # loudness >= 2:
-        logging.getLogger().setLevel(logging.DEBUG)
+        level = logging.INFO
+    else:  # loudness >= 1
+        level = logging.DEBUG
+    logging.basicConfig(
+        level=level, format="%(levelname)s: %(message)s"
+    )
 
     installer = NativeInstaller(destdir=args.destdir)