core: Unable to restore from 3.1 LogCollector...

Unable to restore from 3.1 LogCollector DB backup file

In the case that restore is done from a TAR file we should try to
install the plpgsql language as well.

Change-Id: I543679f87bc9fd0f26909db3889dee482dfada77
Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=960760
Signed-off-by: Eli Mesika <emesika@redhat.com>