The pre-install operations may fail, yet that failure is not
elevated to the user. This masks the failure and makes early
package install issues difficult to troubleshoot.
If the basic pre-install script fails, the charm should not
proceed to later hooks as the requirements may not be met.
Hashbangs for bash should specify -e (errexit) on all of the
pre-install bash scripts.
Change-Id: I4e03103789100aca944ad79d2e59abfa6a65ab3f
Closes-bug: #1815243
Partial-bug: #1815231
Alex Kavanagh