Generic RPM installation detection

This is an alternative to I77957e9a107f0b1aeef81fb6a98e9840954d2a44
which makes detection of RPM-based distros a little more generic.

After some thought, this seems to be a pretty low-level and generic
way to match what we want right now; i.e. centos, fedora & related
rhel-based distros like cloudos).

The will all have a /etc/*-release file managed by RPM, and all
non-relevant systems (debian/ubuntu) will not (even if they somehow
managed to get rpm installed, for alien or something).

Change-Id: If2bd38df2a9720aa9288aa522b7587136e900d93

functions.sh

@@ -20,9 +20,15 @@ SUDO="sudo"
 
 # Distro check functions
 function is_fedora {
-    # note we consider CentOS 7 as fedora for now
-    lsb_release -i 2>/dev/null | grep -iq "fedora" || \
-        lsb_release -i 2>/dev/null | grep -iq "CentOS"
+    # note this is a little mis-named, we consider basically anything
+    # using RPM as "is_fedora".  This includes centos7, fedora &
+    # related distros like CloudOS and OracleLinux (note, we don't
+    # support centos6 with this script -- we are assuming is_fedora
+    # implies >=centos7 features such as systemd/journal, etc).
+    #
+    # This is KISS; if we need more fine-grained differentiation we
+    # will handle it later.
+    rpm -qf /etc/*-release >&/dev/null
 }
 
 function is_ubuntu {