support setting apollo.cacheDir from app.properties

[erystasius]

Fixes #2306

[codecov-io]

Codecov Report

Merging #2317 into master will decrease coverage by 0.04%.
The diff coverage is 100%.

@@             Coverage Diff              @@
##             master    #2317      +/-   ##
============================================
- Coverage     49.99%   49.94%   -0.05%     
  Complexity     1981     1981              
============================================
  Files           402      402              
  Lines         12400    12402       +2     
  Branches       1273     1274       +1     
============================================
- Hits           6199     6194       -5     
- Misses         5758     5765       +7     
  Partials        443      443

Impacted Files	Coverage Δ	Complexity Δ
...va/com/ctrip/framework/apollo/util/ConfigUtil.java	94.57% <100%> (+0.08%)	49 <0> (+1)	⬆️
...work/apollo/biz/message/DatabaseMessageSender.java	56.25% <0%> (-10.42%)	6% <0%> (-2%)
...mework/apollo/portal/component/PortalSettings.java	65.07% <0%> (-4.77%)	5% <0%> (ø)
.../apollo/internals/RemoteConfigLongPollService.java	80.24% <0%> (+0.61%)	28% <0%> (+1%)	⬆️

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[coveralls]

Coverage decreased (-0.05%) to 53.516% when pulling 7b9f0f4 on erystasius:cache-dir-from-app-properties into 89c370e on ctripcorp:master.

[nobodyiam]

LGTM