Use getpwnam() instead of AID_* macros

AID_* values are defined in libcutils private headers and hence
is not exported. Use getpwnam() instead to get these values.

Test: pass
Bug: 63135587
Change-Id: I748019e5351be9b386a2dec2e3ca7b613cc6732d
Merged-In: I748019e5351be9b386a2dec2e3ca7b613cc6732d
2 files changed