[CLI] options to unset default checkers and to print active checkers
Summary:
Demo:
```
$ infer -a checkers --print-active-checkers
Found 1 source file to analyze in /home/jul/infer/infer-out
Active checkers: annotation reachability, fragment retains view, immutable cast, printf args, quandary, SIOF, thread safety
Starting analysis...
[...]
$ infer -a checkers --print-active-checkers --no-default-checkers
Found 1 source file to analyze in /home/jul/infer/infer-out
Active checkers: none
[...]
$ infer -a checkers --print-active-checkers --no-default-checkers --bufferoverrun
Found 1 source file to analyze in /home/jul/infer/infer-out
Active checkers: buffer overrun
[...]
$ infer -a checkers --print-active-checkers --no-default-checkers --bufferoverrun --default-checkers --biabduction --no-siof
Found 1 source file to analyze in /home/jul/infer/infer-out
Active checkers: annotation reachability, biabduction, buffer overrun, fragment retains view, immutable cast, printf args, quandary, thread safety
[...]
```
Reviewed By: jeremydubreil
Differential Revision: D5095657
fbshipit-source-id: 8043b00
Jules Villard
b964f6ab74