use hostname and path flags in all of the CLI

[tangiel]

App Engine is deprecating app IDs in config and we want to get away from this model anyway. This change adds --hostname and --path to get-discovery-doc and get-client-lib to fully specify where an API is hosted. This involves the following code changes:

• refactor of ServiceContext to allow specifying a hostname instead of just an app id
• Renamed the appHostName property to appHostname in ServiceContext
• debug flag in get-discovery-doc is now a no-op. It really already was, but now it has been removed from the code except for the interface itself so we don't break anyone. It stopped outputting intermediate files because there no longer are any.
• small cleanups (removed extra space, unused CLI options, test formatting adjustments)

[codecov-io]

Codecov Report

Merging #83 into master will increase coverage by 0.04%. The diff coverage is 78.94%.

@@             Coverage Diff              @@
##             master      #83      +/-   ##
============================================
+ Coverage      79.4%   79.45%   +0.04%     
- Complexity     1618     1619       +1     
============================================
  Files           154      154              
  Lines          5449     5457       +8     
  Branches        702      702              
============================================
+ Hits           4327     4336       +9     
+ Misses          848      846       -2     
- Partials        274      275       +1

Impacted Files	Coverage Δ	Complexity Δ
...ogle/api/server/spi/tools/EndpointsToolAction.java	86.39% <ø> (+0.68%)	44 <0> (+1)	:arrow_up:
.../google/api/server/spi/config/model/ApiConfig.java	94.44% <ø> (ø)	67 <0> (ø)	:arrow_down:
...oogle/api/server/spi/tools/GetClientLibAction.java	76.92% <100%> (+1.92%)	3 <0> (ø)	:arrow_down:
...java/com/google/api/server/spi/ServiceContext.java	83.33% <75%> (-0.88%)	11 <7> (ø)
...le/api/server/spi/tools/GetDiscoveryDocAction.java	32.14% <80%> (+3.05%)	3 <0> (ø)	:arrow_down:

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