[SPARK-7444] [TESTS] Eliminate noisy css warn/error logs for UISeleniumSuite
Eliminate the following noisy logs for `UISeleniumSuite`:
```
15/05/07 10:09:50.196 pool-1-thread-1-ScalaTest-running-UISeleniumSuite WARN DefaultCssErrorHandler: CSS error: 'http://192.168.0.170:4040/static/bootstrap.min.css' [793:167] Error in style rule. (Invalid token "*". Was expecting one of: <EOF>, <S>, <IDENT>, "}", ";".)
15/05/07 10:09:50.196 pool-1-thread-1-ScalaTest-running-UISeleniumSuite WARN DefaultCssErrorHandler: CSS warning: 'http://192.168.0.170:4040/static/bootstrap.min.css' [793:167] Ignoring the following declarations in this rule.
15/05/07 10:09:50.197 pool-1-thread-1-ScalaTest-running-UISeleniumSuite WARN DefaultCssErrorHandler: CSS error: 'http://192.168.0.170:4040/static/bootstrap.min.css' [799:325] Error in style rule. (Invalid token "*". Was expecting one of: <EOF>, <S>, <IDENT>, "}", ";".)
15/05/07 10:09:50.197 pool-1-thread-1-ScalaTest-running-UISeleniumSuite WARN DefaultCssErrorHandler: CSS warning: 'http://192.168.0.170:4040/static/bootstrap.min.css' [799:325] Ignoring the following declarations in this rule.
15/05/07 10:09:50.198 pool-1-thread-1-ScalaTest-running-UISeleniumSuite WARN DefaultCssErrorHandler: CSS error: 'http://192.168.0.170:4040/static/bootstrap.min.css' [805:18] Error in style rule. (Invalid token "*". Was expecting one of: <EOF>, <S>, <IDENT>, "}", ";".)
15/05/07 10:09:50.198 pool-1-thread-1-ScalaTest-running-UISeleniumSuite WARN DefaultCssErrorHandler: CSS warning: 'http://192.168.0.170:4040/static/bootstrap.min.css' [805:18] Ignoring the following declarations in this rule.
```
Author: zsxwing <zsxwing@gmail.com>
Closes #5983 from zsxwing/SPARK-7444 and squashes the following commits:
4202728 [zsxwing] Add SparkUICssErrorHandler for all tests
d1398ad [zsxwing] Merge remote-tracking branch 'origin/master' into SPARK-7444
7bb7f11 [zsxwing] Merge branch 'master' into SPARK-7444
a59f40e [zsxwing] Eliminate noisy css warn/error logs for UISeleniumSuite
95690a17d3