Description of problem:

If an user is used to authenticate against the "/query/task" endpoint and when querying for tasks using potentialOwner parameter, does not matter the value for the potential owner parameter, it returns all the task considering the authenticated user as the potential owner.

Version-Release number of selected component (if applicable):
n/a

How reproducible:
always

Steps to Reproduce:
1. Create an user with roles admin, g1 and g2
2. Deploy process with human tasks with group g1 and g2
3. Use the query/task endpoint to query for tasks using potentialOwner with a random value:

curl -X GET -u 'g1g2user:redhat2014!' http://localhost:8080/business-central/rest/query/task?potentialOwner=somerandomvalue

Actual results:

It returns all tasks where the user is potential owner:

$ curl -X GET -u 'g1g2user:redhat2014!' http://localhost:8080/business-central/rest/query/task?potentialOwner=somerandomvalue
<?xml version="1.0" encoding="UTF-8" standalone="yes"?><task-summary-list-response><task-summary><id>9</id><name>G2 HT</name><subject>G2 HT</subject><description></description><status>Ready</status><priority>0</priority><skipable>true</skipable><created-on>2015-09-10T13:07:36.050-03:00</created-on><activation-time>2015-09-10T13:07:36.050-03:00</activation-time><process-instance-id>16</process-instance-id><process-id>ht_tests.proc2_ht</process-id><process-session-id>16</process-session-id><deployment-id>example:ht_tests:1.0</deployment-id><quick-task-summary>false</quick-task-summary><parent-id>-1</parent-id></task-summary><task-summary><id>10</id><name>ht</name><subject>ht</subject><description></description><status>Ready</status><priority>0</priority><skipable>true</skipable><created-on>2015-09-10T13:07:40.217-03:00</created-on><activation-time>2015-09-10T13:07:40.217-03:00</activation-time><process-instance-id>17</process-instance-id><process-id>ht_tests.proc_ht</process-id><process-session-id>17</process-session-id><deployment-id>example:ht_tests:1.0</deployment-id><quick-task-summary>false</quick-task-summary><parent-id>-1</parent-id></task-summary></task-summary-list-response>

Expected results:

Only the tasks with potential owner equal the parameter should be returned.

Additional info:

This does not happen when we use other parameters such as processId.