tools_common.sh: Correct the source_version() func

version.cmake strips optional prefix before the version. So,
source_version() function needs to do the same, so that the strings can
be matched.

Before this, for any commit after research-v1.0.0 anchor, it used to
give incorrect warnings like the one below:

"Warning: version has changed since last cmake run.
  cmake version: v1.0.0-114-g4dcb6b040 version now:
  research-v1.0.0-114-g4dcb6b040"

Change-Id: I0a61c476d59e8f349ca798dd1781bbb27846ca80
diff --git a/test/tools_common.sh b/test/tools_common.sh
index d40709b..9646e50 100755
--- a/test/tools_common.sh
+++ b/test/tools_common.sh
@@ -88,10 +88,13 @@
 
 # Echoes current git version as reported by running 'git describe', or the
 # version used by the cmake build when git is unavailable.
+# Note: version.cmake strips optional prefix before the version. So,
+# source_version() function needs to do the same, so that the strings can be
+# compared in check_version_strings() later.
 source_version() {
   if git --version > /dev/null 2>&1; then
     (cd "$(dirname "${0}")"
-    git describe)
+    git describe | sed 's/.*-v/v/')
   else
     cmake_version
   fi