Fix error when no custom config file matches *.conf.sample

In generate_sample.sh, an error will be raised when no custom config
files match '$BASEDIR/tools/config/*.conf.sample', because CONCAT_FILE
will be set with value '$BASEDIR/tools/config/*.conf.sample'.

for CONCAT_FILE in $BASEDIR/tools/config/*.conf.sample; do

    cat $CONCAT_FILE >> $OUTPUTFILE

done

This path will check match result first to avoid the error.

Closes-Bug: #1251297
Change-Id: I4bb2036b1d385e8f7621cbd8b14134f12618230d
Run generate_sample.sh as part of tox tests

Right now there is no guarantee that any changes to the sample
config generation code actually work.  Even though Oslo doesn't
need a sample config, run the script anyway to at least catch
major errors.

Change-Id: If63f84184c459bc3e2245b7fde19362140243894
Merge "Fix error when no custom config file matches *.conf.sample"
Merge "Run generate_sample.sh as part of tox tests"