This pull request add a bash plugin for TACACS+ per-command authorization
#### Why I did it
1. To support TACACS per command authorization, we check user command before execute it.
2. Fix libtacsupport.so can't parse tacplus_nss.conf correctly issue:
Support debug=on setting.
Support put server address and secret in same row.
3. Fix the parse_config_file method not reset server list before parse config file issue.
#### How I did it
The bash plugin will be called before every user command, and check user command with remote TACACS+ server for per-command authorization.
#### How to verify it
UT with CUnit cover all code in this plugin.
Also pass all current UT.
#### Which release branch to backport (provide reason below if selected)
N/A
#### Description for the changelog
Add Bash TACACS+ plugin.
#### A picture of a cute animal (not mandatory but encouraged)
