Make the value of commit available in custom scripts

[benjy44]

Environment

• Python version: 3.5.1
• NetBox version: 2.7.7

Proposed Functionality

Make the status of commit (True/False) available so it's possible to know if part of a script not directly tied to NetBox should be run or not.

Use Case

I have a script to create VMs in a certain way and I use it to update a text file that contains the IPs of the newly created VMs for external use.
While the script and the file is generated properly, I don't want my file to be updated if the VMs are not actually created, ie: when commit=False.

As a workaround proposed by @steffann I can use if '_commit' in self.request.POST which works fine but a cleaner way would be better.

Database Changes

Don't think so

External Dependencies

none

[samk-acw]

Being able to hide/disable the commit checkbox would also be nice for scripts that don't make any changes (which is essential what reports are, but I believe the custom scripts feature is ultimately meant to replace reports)

[jeremystretch]

Implemented in 5000f7f