apt_key: Fix traceback when key_id format is invalid

Signed-off-by: Philippe Pepiot <phil@philpep.org>
Fix documentation for accept_hostkey
Fix small typo resulting in a traceback for the apt_key module
Rejoin args list into a string for run_command when using an unsafe shell

This allows the use of an args list with leading environment variables,
which otherwise would fail due to the way Popen works.
Revert "Rejoin args list into a string for run_command when using an unsafe shell"

This reverts commit 4273cb2d8ead8f95fa0032da4082ffd7da338472.
Fix typo in run_command when sending data that is not binary
Rejoin args list into a string for run_command when using an unsafe shell

This allows the use of an args list with leading environment variables,
which otherwise would fail due to the way Popen works.
Adding new unit tests for module_utils/basic (run_command only now)
Reset the current directory after running subprocess.Popen
Documentation updates
Be sure to return to the old directory if cwd is set in run_command
Cleaning up some exception blocks in TestModuleUtilsBasic
Updating CHANGELOG/RELEASES in devel for 1.5.3 and older releases
Merge pull request #6477 from angstwad/docs-fix

Documentation updates
Merge pull request #6470 from patrickheeney/doc-git-fix

Fix documentation for accept_hostkey in GIT module
Merge pull request #6468 from philpep/fix_apt_key

apt_key: Fix traceback when key_id format is invalid
Update index.rst
Micro-optimization of inventory.expand_hosts.detect_range
Micro-optimization: replace s.find(x)!=-1 with x in s

timeit shows a speedup of ~3x on Python 2.7.5 x86_64.
It also makes the code a bit shorter.
hostname module: don't filter hostnamectl with awk

There's no need to filter hostnamectl's output with awk because its man
page says:

    hostnamectl [OPTIONS...] {COMMAND}

       --static, --transient, --pretty
	   If status is used (or no explicit command is given) and one
	   of those fields is given, hostnamectl will print out just
           this selected hostname.

E.g. hostnamectl --static status => ansible.example.org