Description of problem:
When plugin property has some value and the new jboss-as7 plugin which does not contain this property is uploaded into RHQ, the plugin property value is not deleted, because when another updated jboss-as7 plugin containing this property is uploaded, the plugin property has the same value as it had at the beginning. 


Version-Release number of selected component (if applicable):
Version: 4.9.0-SNAPSHOT
Build Number: 48f882b

How reproducible:
always

Steps to Reproduce:
1. RHQ system is running (including agent which was discovered and imported).
2. Update jboss-as7 plugin with eg. this plugin-property:

<c:simple-property name="errorMessage_0" type="string" required="false" description="Testing property" />

which includes adding this property into <plugin-configuration> section of section <server> (in certain mode) in file META-INF/rhq-plugin.xml and updating file META-INF/MANIFEST.MF where Implementation-Version should be probably higher than plugin actually contained in RHQ

and upload this plugin into RHQ.

3. Then under EAP resource choose Inventory tab and click on Connection Settings and fill your property errorMessage_0 with eg. value ERROR.


4. Then upload into RHQ jboss-as7 plugin not containing our property errorMessage_0 (its implementation version should be increased).

5. Check that the property errorMessage_0 cannot be visible on page Conections Settings.

6. Then upload analogical way into RHQ jboss-as7 plugin containing our property errorMessage_0.

7. Go to EAP resource choose Inventory tab and click on Connection Settings.



Actual results:
Property errorMessage_0 on page has value ERROR as at the beginning.


Expected results:
Property errorMessage_0 on page has unset value.


Additional info: