packaging: changed psql execution environment

Added LC_ALL=C in the environment provided by getPgPassEnv
used whenever psql is called.
Renamed getPgPassEnv to getPgEnv and added the documentation.

Change-Id: I24869748184d9397192461fa01da632a558208f7
Bug-Url: https://bugzilla.redhat.com/912426
Signed-off-by: Sandro Bonazzola <sbonazzo@redhat.com>