sos: postgresql: always use db host

Previously it was possible to access the database
through unix socket.
Now the access for user engine is limited to tcp connection.
Changed the call to sosreport for passing db host to
postgresql plugin.

Change-Id: Ibb4ac5e03e3b6f1f6d7b499c969bdeb5ed9026cb
Bug-Url: https://bugzilla.redhat.com/1039747
Signed-off-by: Sandro Bonazzola <sbonazzo@redhat.com>