Fix/make streams context aware

[ingar]

Summary

Make the storage network New*Stream calls context-aware, and remove the context.Background() usage.

Resolves #292

[hannahhoward]

LGTM

[codecov-commenter]

Codecov Report

Merging #308 into master will increase coverage by 0.10%.
The diff coverage is 63.64%.

@@            Coverage Diff             @@
##           master     #308      +/-   ##
==========================================
+ Coverage   63.64%   63.74%   +0.10%     
==========================================
  Files          41       41              
  Lines        2582     2578       -4     
==========================================
  Hits         1643     1643              
+ Misses        818      814       -4     
  Partials      121      121              

Impacted Files	Coverage Δ
storagemarket/impl/client.go	3.20% <0.00%> (ø)
storagemarket/impl/clientstates/client_states.go	90.00% <100.00%> (ø)
storagemarket/network/libp2p_impl.go	77.97% <100.00%> (ø)
storagemarket/types.go	0.00% <0.00%> (ø)

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