minor fix for Spring

[nobodyiam]

1. make ApolloAnnotationProcessor run as late as possible
2. make PropertySourcesProcessor run as early as possible
3. fix PropertySourcesProcessor initialization logic to support multple
   Spring contexts

[coveralls]

Coverage remained the same at 49.698% when pulling 9b06053 on nobodyiam:apollo-spring-fix into 6f30d52 on ctripcorp:master.

[codecov-io]

Codecov Report

Merging #560 into master will decrease coverage by -0.02%.
The diff coverage is 100%.

@@             Coverage Diff              @@
##             master     #560      +/-   ##
============================================
- Coverage     46.34%   46.33%   -0.02%     
- Complexity     1360     1361       +1     
============================================
  Files           325      325              
  Lines          8779     8779              
  Branches        841      841              
============================================
- Hits           4069     4068       -1     
  Misses         4417     4417              
- Partials        293      294       +1

Impacted Files	Coverage Δ	Complexity Δ
...o/spring/annotation/ApolloAnnotationProcessor.java	100% <100%> (ø)	12 <2> (+1)	✅
...apollo/spring/config/PropertySourcesProcessor.java	100% <100%> (ø)	11 <6> (+1)	✅
...ervice/service/ReleaseMessageServiceWithCache.java	85.71% <0%> (-1.2%)	24% <0%> (-1%)

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