BUGFIX for Issue 7811: Adding file existence check when performing mysql import on...

Adding file existence check when performing mysql import on a .gz or .bz2 file, otherwise Ansible will not notice that the underlying *nix command silently died.

The following is sample run showing the issue as well as the fix working on a remote system (Ubuntu 12.04 LTS via Vagrant).

Given the following play:
~~~
---
- name: add mysql
  apt: pkg=mysql-server state=present update_cache=true
  sudo: yes
- name: add mysqldb python module
  apt: pkg=python-mysqldb state=present
  sudo: yes
- name: ensure database exists
  mysql_db: name=testdb state=present
  sudo: yes
- name: import data from existent file
  mysql_db: name=testdb state=import target=/tmp/exists.sql.gz
  sudo: yes
- name: import data from non-existent file
  mysql_db: name=testdb state=import target=/tmp/missing.sql.gz
  sudo: yes
~~~

**Note: This assumes you have already performed ``$ touch /tmp/exists.sql && gzip /tmp/exists`` on the remote system.**

Ansible will run it without error even though the file does not exist:
~~~
==> default: Running provisioner: ansible...

PLAY [run bugfix provisioning] ************************************************

GATHERING FACTS ***************************************************************
ok: [default]

TASK: [bugfix | add mysql] ****************************************************
ok: [default]

TASK: [bugfix | add mysqldb python module] ************************************
changed: [default]

TASK: [bugfix | ensure database exists] ***************************************
changed: [default]

TASK: [bugfix | import data from non-existent file] ***************************
changed: [default]

PLAY RECAP ********************************************************************
default                    : ok=5    changed=3    unreachable=0    failed=0
~~~

But after applying the fix to the code and adding an existence check using the ``test`` unix command, Ansible starts failing on non-existent files but still succeeding on files that exist in the system:
~~~
==> default: Running provisioner: ansible...

PLAY [run bugfix provisioning] ************************************************

GATHERING FACTS ***************************************************************
ok: [default]

TASK: [bugfix | add mysql] ****************************************************
ok: [default]

TASK: [bugfix | add mysqldb python module] ************************************
ok: [default]

TASK: [bugfix | ensure database exists] ***************************************
ok: [default]

TASK: [bugfix | import data from existent file] *******************************
changed: [default]

TASK: [bugfix | import data from non-existent file] ***************************
failed: [default] => {"failed": true, "item": ""}

FATAL: all hosts have already failed -- aborting

PLAY RECAP ********************************************************************
           to retry, use: --limit @/Users/scott/playbook.retry

default                    : ok=5    changed=1    unreachable=0    failed=1

Ansible failed to complete successfully. Any error output should be
visible above. Please fix these errors and try again.
~~~

Although Ansible is now responding correctly to non-existent files, the only downside of this approach is that the ``test`` command does not respond with an error message, so Ansible cannot tell the end-user why the task failed.

**Note: I am using ``test -e`` as a test for pure file existence.  I am not making any other assumptions about the type of file.**