Log: libcrmcommon: Drop crm_perror() in acl.c

• Set errno to 0 before calling getpwuid(), as the man page instructs.
• Improve error message, noting that errno might not get set.
• Use correct format specifier for uid_t.
• Log at error level instead of info level, since the callers log errors if this fails.
• Call pcmk__uid2username() in crm_log_init(), avoiding duplication.
• Compare user names case-sensitively in crm_log_init().
• Error-check and log an error for pcmk__uid2username() in cibadmin.c.

The only thing we lose here is writing the message to stderr for CLI
tools. However, CLI tools have verbose options.

Ref T172

Signed-off-by: Reid Wahl <nrwahl@protonmail.com>