If a executable is defined but not found the module should fail.

If a executable is defined but not found the module should fail. Addresses https://github.com/ansible/ansible/issues/5781.

Added info on --skip-tags to tags documentation.

Using dict(k=v) means the key was always named 'k', as the variable
is not interpreted there.

Fixes #5801

Mention shell module in command documentation

Update wait_for documentation - remove extra quote

Fixed typo

Used the twice in a row

Fix broken Tower links

Also note AWX is named "Tower" now, as we found that simpler.

In particular, do not rely on the $USER environment variable always existing.
tmux for example seems to clear it, causing lots of invalid messages:
"previous known host file not found"

This broke in commit 80fd22dc, but instead of reverting that commit, we now
fall back to expanding just ~ when $USER is not set.

be permissive with BSD with service enabled upper/lower/mixed cases

Signed-off-by: Brian Coca <briancoca+ansible@gmail.com>

su_user_var.  My last PR was only half merged, and when the bug fix for
the su/su_pass typo was merged, the removed line in this commit was
mistakenly reintroduced.

Added ability to create EC2 volume from snapshot

Add skip_tags to ansible-playbook man page

Merge branch 'feat/ec2_start_stop' of git://github.com/Geryon/ansible into Geryon-feat/ec2_start_stop