extmgr: Add logging for extension load/initialize

Easier to track what extension may misbehave.

Bug-Url: https://bugzilla.redhat.com/show_bug.cgi?id=1120720
Change-Id: I03169863db00b5bf4ac5f827fbd0aebcf73a51f3
Signed-off-by: Alon Bar-Lev <alonbl@redhat.com>