Wrap SSHTunnelForward and make it MSONable

[shyamd]

This PR makes the ssh tunnel feature MSONable so that we can serialize and deserialize this information.

[lgtm-com]

This pull request introduces 2 alerts when merging a1d97b5 into 0243662 - view on LGTM.com

new alerts:

• 1 for Unused import
• 1 for Binding a socket to all network interfaces

[codecov]

Codecov Report

Merging #320 into master will decrease coverage by 1.10%.
The diff coverage is 36.00%.

@@            Coverage Diff             @@
##           master     #320      +/-   ##
==========================================
- Coverage   88.49%   87.39%   -1.11%     
==========================================
  Files          28       28              
  Lines        2121     2165      +44     
==========================================
+ Hits         1877     1892      +15     
- Misses        244      273      +29     

Impacted Files	Coverage Δ
src/maggma/api/APIManager.py	72.09% <ø> (ø)
src/maggma/api/resource.py	98.14% <ø> (ø)
src/maggma/utils.py	93.96% <ø> (ø)
src/maggma/stores/mongolike.py	81.58% <34.69%> (-12.04%)	⬇️
src/maggma/api/query_operator.py	83.50% <100.00%> (ø)
src/maggma/stores/aws.py	84.61% <0.00%> (+2.11%)	⬆️

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