ADD jsonCheck.sh script

It seems to work, as is now detecting 3 files that have JSON formatting problems:

```
fermin@oriondeb:~/src/fiware-orion/test/jsonCheck$ ./jsonCheck.sh 
Expecting property name: line 17 column 4 (char 232)
File /home/fermin/src/fiware-orion/test/unittests/testData/discoverContextAvailabilityRequest_parseError.json is not a well-formed JSON document
Expecting property name: line 19 column 1 (char 243)
File /home/fermin/src/fiware-orion/test/unittests/testData/queryContextRequest_noRestriction.json is not a well-formed JSON document
Expecting property name: line 24 column 4 (char 353)
File /home/fermin/src/fiware-orion/test/unittests/testData/queryContextRequest_noScopeValue.json is not a well-formed JSON document
```

Do we want to fix these 3 as part of this PR?

In addition, note that the makefile target xml_check has changed to have a name that covers both XML and JSON cases. This probably make Jenkins cry upon this PR merging, but I will next fix Jenkins after that.