Added a check further to make the services to stop appropriately before unmount.

Fix #4651

Optimizing number of calls made to sonic-cfggen during service
start up as it adds to total system boot up time.

signed-off-by: Tamer Ahmed <[email protected]>

**- Why I did it**
sonic-cfggen call is slow and it adds to system start up time

**- How I did it**
places all required variable into single template and called into sonic-cfggen using this template

**- How to verify it**
***-Test 1***
there is an average saving of .5 to 1 sec between old script and new script
```
root@str-s6000-acs-14:/# time ./orchagent_old.sh
/usr/bin/orchagent -d /var/log/swss -b 8192 -m f4:8e:38:16:bc:8d

real	0m3.546s
user	0m2.365s
sys	0m0.585s

root@str-s6000-acs-14:/# time ./orchagent_new.sh
/usr/bin/orchagent -d /var/log/swss -b 8192 -m f4:8e:38:16:bc:8d

real	0m2.058s
user	0m1.650s
sys	0m0.363s
```
***-Test 2***
Built an image with this change and orchagent is running with intended params:
```
admin@str-s6000-acs-14:~$ ps -ef | grep orchagent
root      2988  1901  1 02:09 pts/0    00:00:02 /usr/bin/orchagent -d /var/log/swss -b 8192 -m f4:8e:38:16:bc:8d
```

signed-off-by: Tamer Ahmed <[email protected]>

Added xmltodict and jsondiff packages needed to run vs test cases successfully for DPB.
sonic-utilities PR #766 has a dependency on these packages.

Signed-off-by: Sangita Maity <[email protected]>