Switch to filtering DescribeNetworkInterfaces based on AZs, not VPCs

[sargun]

No description provided.

[coveralls]

Pull Request Test Coverage Report for Build 1869

• 0 of 51 (0.0%) changed or added relevant lines in 2 files are covered.
• 2 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.1%) to 23.888%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
vpc/ec2wrapper/ec2metadata.go	0	6	0.0%
vpc/globalgc/globalgc.go	0	45	0.0%

Files with Coverage Reduction	New Missed Lines	%
vpc/globalgc/globalgc.go	2	0.0%

Totals
Change from base Build 1860:	-0.1%
Covered Lines:	2288
Relevant Lines:	9578

---

💛 - Coveralls

[codecov]

Codecov Report

Merging #166 into master will decrease coverage by 0.16%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##           master     #166      +/-   ##
==========================================
- Coverage   33.73%   33.56%   -0.17%     
==========================================
  Files          63       63              
  Lines        7551     7588      +37     
==========================================
  Hits         2547     2547              
- Misses       4697     4734      +37     
  Partials      307      307

Impacted Files	Coverage Δ
vpc/globalgc/globalgc.go	0% <0%> (ø)	⬆️
vpc/ec2wrapper/ec2metadata.go	0% <0%> (ø)	⬆️

[fabiokung]

LGTM

A followup PR to remove commented code and remove the vpcID param would be good once we determine that this fixes the issue with filtering Describes.