Rerun command

[shabazpatel]

1. Adding rerun command which checks out to the snapshot version of the run specified and then runs the experiment command as given. It finds the "core snapshot" for the run and uses that as the basis as specified in the "_get_core_snapshot" function for the run controller.

[coveralls]

Pull Request Test Coverage Report for Build 800

• 38 of 43 (88.37%) changed or added relevant lines in 3 files are covered.
• 53 unchanged lines in 16 files lost coverage.
• Overall coverage decreased (-1.2%) to 86.966%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
datmo/cli/command/run.py	36	38	94.74%
datmo/cli/main.py	0	3	0.0%

Files with Coverage Reduction	New Missed Lines	%
datmo/cli/command/base.py	1	91.55%
datmo/snapshot.py	1	82.41%
datmo/core/controller/file/driver/local.py	2	90.98%
datmo/cli/command/datmo_command.py	2	80.0%
datmo/core/util/i18n.py	2	85.71%
datmo/cli/command/run.py	2	73.6%
datmo/task.py	2	91.6%
datmo/core/controller/code/driver/file.py	2	94.32%
datmo/cli/command/snapshot.py	2	98.79%
datmo/cli/command/session.py	2	93.55%

Totals
Change from base Build 792:	-1.2%
Covered Lines:	3890
Relevant Lines:	4473

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💛 - Coveralls