Set the shell variable on the ssh connection type for accelerated mode

Fixes #8799
The correct option is password_file. Fixes #8752
Merge variables for hosts instead of updating in get_variables()
Make sure group_vars/all is loaded for ungrouped hosts

Fixes #6563
Convert boolean strings from set_fact to proper boolean values

Also adds integration tests for booleanification of strings

Fixes #8629
Fixing multiline parsing to preserve newlines

Fixes #8813
Fix quoting issues in lineinfile for individual single-quotes

Fixes #8806
Ensure checkmode is honored for templates that haven't changed

Fixes #8998
Ensure remote files are chmod'd properly for su/su_user too

Fixes #8594
Before decrypting check if vault password is set or error early

Fixes #8926
Fix #7711

Fix relative symlinks creation in file module

Signed-off-by: Oleg Bulatov <oleg@bulatov.me>
Version bump for release 1.7.2
Removing symbolic mode tests, which are not in the 1.7.x branch
Include el7 mariadb support in mysql integration test
Correct mysql integration indentation
Add mongodb_replica_set module for managing MongoDB replica sets