Put devstack-version info into separate file

As a follow on to I4c269a7f3d63ee9a976e7c3636fc3e5e8dab9ae3; the
quoting gets tricky when putting arbitrary command-substitution
strings into saved echo-able strings.  As they say, "the only winning
move is not to play" :)

An alternative proposal is to not write this into a script but just
dump info into a file.  To my mind, this has several advantages --
avoid getting involved in quoting, not dropping a script into the
global environment -- it's just as easy to "cat" -- and the plain-text
file can be collected as an artifact during log collection (also moved
git commit line to separate line for easier parsing during log search,
etc).

-- Note

This is a combined cherry-pick of the following

 2c0faca038 - add version
 3415521d56 - fix to ^
 07cbc44942 - this change

2c0faca and 3415522 were not merged to this branch at the time to
avoid breakage.  This brings consistency across the open branches.

Change-Id: Ic7391dd087657c0daf74046e4a052c53f4eb6e1a

functions

@@ -691,6 +691,18 @@ function enable_kernel_bridge_firewall {
     done
 }
 
+# Save some state information
+#
+# Write out various useful state information to /etc/devstack-version
+function write_devstack_version {
+    cat - > /tmp/devstack-version <<EOF
+DevStack Version: ${DEVSTACK_SERIES}
+Change: $(git log --format="%H %s %ci" -1)
+OS Version: ${os_VENDOR} ${os_RELEASE} ${os_CODENAME}
+EOF
+    sudo install -m 644 /tmp/devstack-version /etc/devstack-version
+    rm /tmp/devstack-version
+}
 
 # Restore xtrace
 $_XTRACE_FUNCTIONS

stack.sh

@@ -190,6 +190,9 @@ if [[ ! -r $TOP_DIR/stackrc ]]; then
 fi
 source $TOP_DIR/stackrc
 
+# write /etc/devstack-version
+write_devstack_version
+
 # Warn users who aren't on an explicitly supported distro, but allow them to
 # override check and attempt installation with ``FORCE=yes ./stack``
 if [[ ! ${DISTRO} =~ (trusty|xenial|yakkety|7.0|wheezy|sid|testing|jessie|f23|f24|f25|rhel7|kvmibm1) ]]; then
@@ -1454,6 +1457,10 @@ if [[ -n "$DEPRECATED_TEXT" ]]; then
     echo_summary "WARNING: $DEPRECATED_TEXT"
 fi
 
+# Useful info on current state
+cat /etc/devstack-version
+echo
+
 # Indicate how long this took to run (bash maintained variable ``SECONDS``)
 echo_summary "stack.sh completed in $SECONDS seconds."
 

stackrc

@@ -216,6 +216,7 @@ REQUIREMENTS_DIR=$DEST/requirements
 # Setting the variable to 'ALL' will activate the download for all
 # libraries.
 
+DEVSTACK_SERIES="ocata"
 
 ##############
 #