Quiet the xcodebuild logs and run in parallel

[Yasumoto]

Reported by @adam-fowler

[codecov]

Codecov Report

Merging #64 into master will decrease coverage by 0.59%.
The diff coverage is n/a.

@@            Coverage Diff            @@
##           master      #64     +/-   ##
=========================================
- Coverage   48.74%   48.14%   -0.6%     
=========================================
  Files          37       37             
  Lines        4187     4187             
=========================================
- Hits         2041     2016     -25     
- Misses       2146     2171     +25

Impacted Files	Coverage Δ
Sources/AWSSDKSwiftCore/HTTPClient.swift	60% <0%> (-27.78%)	⬇️

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