apt_key: Fix traceback when key_id format is invalid

Signed-off-by: Philippe Pepiot <phil@philpep.org>
Fix documentation for accept_hostkey
[test_ec2*] cloud integration test updates

To support parallel cloud test execution, create and provide a random string to
cloud integration tests.  The variable 'resource_prefix' can be used in cloud
roles and during resource cleanup to safely create/destroy cloud-based
resources.

Additional changes include:

 * The roles test_ec2_key and test_ec2_group were updated to use to
 {{resource_prefix}}.

 * Additionally, the Makefile was updated to set resource_prefix to a random
 string.  The Makefile will also use 'resource_prefix' during cloud_cleanup.

 * All test_ec2* roles were updated to add 'setup_ec2' as a role dependency.
Add an ast.parse unit test for modules to simulate ansible-doc
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
Properly catch import errors in apt

When one accidentally tries to run this module as a user, he gets the error message that python-apt must be installed, no matter what. Because importing apt will trigger an exception as a regular user. Explicitly catching the ImportError will let the exception bubble. The exception clearly says Permission denied somewhere, and the user has a better idea, what he must fix.