Copy of #16565 without the DB migration and priorities renumbering, focusing on the search ext method fix.

Cloned from https://bugzilla.redhat.com/show_bug.cgi?id=1372069
Description of problem:
Searches with global parameters not working as expected. The hammer host list --search "params.globalparameter = value1" returns all hosts even when we override these values for some hosts. From WebUI also we get same results.

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

How reproducible:
Everytime

Steps to Reproduce:
1. hammer global-parameter set --name myparam --value one

2. hammer host set-parameter --host-id 3 --name myparam --value two

3. hammer host list --search "params.myparam = two"
---|-------------------|------------------|------------|-----------------|------------------
ID | NAME | OPERATING SYSTEM | HOST GROUP | IP | MAC
---|-------------------|------------------|------------|-----------------|------------------
3 | testvm.labs.local | RedHat 7.2 | provhg | 192.168.124.100 | 52:54:00:79:93:27
---|-------------------|------------------|------------|-----------------|------------------

4. hammer host list --search "params.myparam = one"
---|----------------------|------------------|------------|-----------------|------------------
ID | NAME | OPERATING SYSTEM | HOST GROUP | IP | MAC
---|----------------------|------------------|------------|-----------------|------------------
1 | satellite.labs.local | RedHat 7.2 | | 192.168.124.10 | 52:54:00:98:78:a0
3 | testvm.labs.local | RedHat 7.2 | provhg | 192.168.124.100 | 52:54:00:79:93:27
---|----------------------|------------------|------------|-----------------|------------------

Expected results: Hosts with values overridden should not be listed