[Minor]ignore all config files in conf

Some config files in ```conf``` should ignore, such as
        conf/fairscheduler.xml
        conf/hive-log4j.properties
        conf/metrics.properties
...
So ignore all ```sh```/```properties```/```conf```/```xml``` files

Author: wangfei <[email protected]>

Closes apache#2395 from scwf/patch-2 and squashes the following commits:

3dc53f2 [wangfei] duplicate ```conf/*.conf```
3c2986f [wangfei] ignore all config files

Author: scwf

.gitignore

@@ -15,11 +15,10 @@ out/
 third_party/libmesos.so
 third_party/libmesos.dylib
 conf/java-opts
-conf/spark-env.sh
-conf/streaming-env.sh
-conf/log4j.properties
-conf/spark-defaults.conf
-conf/hive-site.xml
+conf/*.sh
+conf/*.properties
+conf/*.conf
+conf/*.xml
 docs/_site
 docs/api
 target/
@@ -50,7 +49,6 @@ unit-tests.log
 /lib/
 rat-results.txt
 scalastyle.txt
-conf/*.conf
 scalastyle-output.xml
 
 # For Hive