Transport + storage changes

[lzchen]

Similar to OpenCensus.

1. Silences all exceptions thrown in storage.py
2. Changes default storage_path to tmpdirectory + 'opentelemetry-python' + ikey
3. Adds a more descriptive warning on request timeout to AI endpoint

[codecov-commenter]

Codecov Report

Merging #100 into master will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##           master     #100   +/-   ##
=======================================
  Coverage   92.71%   92.71%           
=======================================
  Files          21       21           
  Lines        1139     1139           
  Branches      144      140    -4     
=======================================
  Hits         1056     1056           
  Misses         55       55           
  Partials       28       28           

Impacted Files	Coverage Δ
azure_monitor/src/azure_monitor/export/__init__.py	100.00% <100.00%> (ø)
azure_monitor/src/azure_monitor/options.py	100.00% <100.00%> (ø)
azure_monitor/src/azure_monitor/storage.py	99.28% <100.00%> (-0.03%)	⬇️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update bc1b053...fe1bbac. Read the comment docs.