Bug fix for PHP client POST (model) and add more PHP test cases

[wing328]

• fixed [BUG] PHP client cannot post model (json) #657
• added test cases for updatePet (POST model) and updatePetWithForm (POST form)
• add pom.xml for integration test

Test result:

SwaggerClient-php|add_php_unit_test⚡ ⇒ mvn integration-test -rf :PhpPetstoreClientTests
[INFO] Scanning for projects...
[INFO]                                                                         
[INFO] ------------------------------------------------------------------------
[INFO] Building PHP Swagger Petstore Client 1.0-SNAPSHOT
[INFO] ------------------------------------------------------------------------
[INFO] 
[INFO] --- maven-dependency-plugin:2.8:copy-dependencies (default) @ PhpPetstoreClientTests ---
[INFO] 
[INFO] --- exec-maven-plugin:1.2.1:exec (bundle-install) @ PhpPetstoreClientTests ---
Loading composer repositories with package information
Installing dependencies (including require-dev) from lock file
Nothing to install or update
Generating autoload files
[INFO] 
[INFO] --- exec-maven-plugin:1.2.1:exec (bundle-test) @ PhpPetstoreClientTests ---

PHPUnit 4.6.4 by Sebastian Bergmann and contributors.

.....

Time: 4.13 seconds, Memory: 5.50Mb

OK (5 tests, 339 assertions)
[INFO] ------------------------------------------------------------------------
[INFO] BUILD SUCCESS
[INFO] ------------------------------------------------------------------------
[INFO] Total time: 6.220 s
[INFO] Finished at: 2015-04-17T20:01:02+08:00
[INFO] Final Memory: 11M/245M
[INFO] ------------------------------------------------------------------------