Set LC_ALL in disk-image-create

It seems that the redhat nodepool job is quite reliably geting a
"floating point" error during centos image build.  This happens after
03-yum-cleanup which is pruning the locales.  This might be a
red-herring, since the logs are full of

  /bin/bash: warning: setlocale: LC_ALL: cannot change locale (C.UTF-8)

I think in our recent de-puppetisation of hosts, something might have
changed that is setting LC_ALL=C.UTF-8 for the jenkins user, at least
on Ubuntu.  This is a problem for centos, as it doesn't have C.UTF-8
locale.  I then think using the invalid locale is what leads the the
floating-point error when doing some maths in dib-run-parts to
calculate runtimes.

We are currently overriding LANG, but we really want LC_ALL to ensure
this applies globally.

Change-Id: I8e7cae093c4b32e0d20b73ae0086f14c7cc6a9cb

diskimage_builder/lib/disk-image-create

@@ -16,9 +16,13 @@
 
 set -eE
 
-# Prevent perl from complaining a lot, but also remove any unexpected side-effects
-# of $LANG varying between build hosts
-export LANG=C
+# Set/override locale.  This ensures consistency in sorting etc.  We
+# need to choose a lowest-common denominator locale, as this is
+# applied when running in the building chroot too (maybe a bug and we
+# should prune this?).  Thus "C" --centOS 7 doesn't include C.utf-8
+# (fedora does, centos 8 probably will).  Note: LC_ALL to really
+# override this; it overrides LANG and all other LC_ vars
+export LC_ALL=C
 
 # Store our initial environment and command line args for later
 export DIB_ARGS="$@"