rsyslog: bump to version 7.6.0

Bumping version of rsyslog and adding new dependencies of liblogging
and libestr.  The first patch has be submitted to the upstream mailing
list and the second patch is a backport from the development branch of
the upstream.

[Peter: needs libuuid / host-pkgconf, fix comment]
Signed-off-by: Clayton Shotwell <clshotwe@rockwellcollins.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>