Rename fetcher/main.cc to fetcher/fetch_cvd.cc

This allows --helpshort to work correctly on the command line.

"--helpshort" relies on there being a file with the same name as the
final binary.

Bug: 137304531
Test: fetch_cvd --helpshort
Change-Id: I37a414a7d95d0b4bbbbac395453cce3d24a1e482
diff --git a/host/commands/fetcher/Android.bp b/host/commands/fetcher/Android.bp
index 4ab6178..11b21af 100644
--- a/host/commands/fetcher/Android.bp
+++ b/host/commands/fetcher/Android.bp
@@ -19,8 +19,8 @@
         "build_api.cc",
         "credential_source.cc",
         "curl_wrapper.cc",
+        "fetch_cvd.cc",
         "install_zip.cc",
-        "main.cc",
     ],
     header_libs: [
         "cuttlefish_glog",
diff --git a/host/commands/fetcher/main.cc b/host/commands/fetcher/fetch_cvd.cc
similarity index 100%
rename from host/commands/fetcher/main.cc
rename to host/commands/fetcher/fetch_cvd.cc