Improve CI test matrix

For Travis CI and GCE, add a naive generator script into a markdown table.
Add GCE/Travis CI matrix docs.
Add CoreOS test cases.
Rework existing cases w/o loosing of coverage.
Rework postinstall tests to support CoreOS as well.

Signed-off-by: Bogdan Dobrelya <bdobrelia@mirantis.com>

scripts/gen_matrix.sh

@@ -0,0 +1,11 @@
+#!/bin/sh
+# Generates MD formatted CI matrix from the .travis.yml
+a=$(perl -ne '/^\s{6}(CLOUD_IMAGE|KUBE_NETWORK_PLUGIN|CLOUD_REGION|CLUSTER_MODE)=(\S+)$/ && print "$2\n"' .travis.yml)
+printf "|%25s|%25s|%25s|%25s|\n" "Network plugin" "OS type" "GCE region" "Nodes layout"
+echo "|-------------------------|-------------------------|-------------------------|-------------------------|"
+c=0
+for i in `echo $a`; do
+  printf "|%25s" $i
+  [ $(($c % 4)) -eq 3 ] && printf "|\n"
+  c=$(( c + 1))
+done