Following the pattern set by tag-route53-hosted-zones.sh. I'm also
following tag-route53-hosted-zones.sh in not testing for any POSIX
commands we use, although it would be easy to add tests for them as
well if we wanted.
At least on Bash 4.4, the -V form writes a missing-command message to
stderr:
$ echo $BASH_VERSION
4.4.23(1)-release
$ command -v does-not-exist >/dev/null
$ command -V does-not-exist >/dev/null
-bash: command: does-not-exist: not found
Because we're not redirecting command's stderr in the script, it will
fall through to the caller's stderr and make it easier for them to
figure out what went wrong.
Also write a "Missing required dependencies" string to stderr. We'd
had a "Dependencies not installed." string literal from 82bdd9fe
(installer/scripts: AWS tag and delete scripts, 2017-06-28,
coreos/tectonic-installer#1239), but it hadn't been written anywhere
so it was effectively an internal comment.
The typos are from 82bdd9fe (installer/scripts: AWS tag and delete
scripts, 2017-06-28, coreos/tectonic-installer#1239).
While I'm touching these lines, also send their output to stderr
instead of stdout (because we're reporting an error).
Also exit nonzero in these unrecognized-option cases.
