Drop support for "kvmibm" distro

The IBM hypervisor distro "KVM for IBM z Systems" gets discontiued,
like announced in March 2017 [1]. The key dates are:

* 03/2017: announcement
* 08/2017: the last day to order (EOM)
* 03/2018: the End of Service (EOL)

As the CI which tests OpenStack with KVM on IBM Z doesn't rely on this
distro anymore and EOM has reached, we remove the Devstack support for
this distro.

This basically reverts commit a5ea08b of Dec 2015.

NOTE: This doesn't affect other distros which have KVM on Z support.

References:
[1] FAQ for KVM for IBM z Systems Delivery Strategy Change
    https://www-01.ibm.com/common/ssi/cgi-bin/ssialias?htmlfid=ZSQ03110USEN&

Change-Id: I009ae4779588615633bff81d0c47a1b879ec9279
diff --git a/functions-common b/functions-common
index c968531..c6ba99e 100644
--- a/functions-common
+++ b/functions-common
@@ -385,8 +385,6 @@
         DISTRO="rhel${os_RELEASE::1}"
     elif [[ "$os_VENDOR" =~ (XenServer) ]]; then
         DISTRO="xs${os_RELEASE%.*}"
-    elif [[ "$os_VENDOR" =~ (kvmibm) ]]; then
-        DISTRO="${os_VENDOR}${os_RELEASE::1}"
     else
         # We can't make a good choice here.  Setting a sensible DISTRO
         # is part of the problem, but not the major issue -- we really
@@ -440,7 +438,7 @@
     [ "$os_VENDOR" = "Fedora" ] || [ "$os_VENDOR" = "Red Hat" ] || \
         [ "$os_VENDOR" = "RedHatEnterpriseServer" ] || \
         [ "$os_VENDOR" = "CentOS" ] || [ "$os_VENDOR" = "OracleServer" ] || \
-        [ "$os_VENDOR" = "Virtuozzo" ] || [ "$os_VENDOR" = "kvmibm" ]
+        [ "$os_VENDOR" = "Virtuozzo" ]
 }