Fix TACACS accounting UT issue caused by auditd log rotate (#11710)

Fix TACACS accounting UT issue caused by auditd log rotate

### Description of PR
Fix TACACS accounting UT issue caused by auditd log rotate

##### Work item tracking
- Microsoft ADO: 26710599

### Type of change

- [x] Bug fix
- [ ] Testbed and Framework(new/improvement)
- [] Test case(new/improvement)

## Approach
#### What is the motivation for this PR?
Fix TACACS accounting UT issue caused by auditd log rotate.
There are 2 code issue:
1. when auditd log rotate, some auditd log will missing from output of 'service auditd status'
1. duthost.command() can only run 1 command, so can't handle piping output to grep

#### How did you do it?
show auditd log with 'sudo journalctl -u auditd --boot' and run command with duthost.shell() to support grep.

#### How did you verify/test it?
Pass all UT

Author: liuh-80

tests/tacacs/utils.py

@@ -315,7 +315,7 @@ def check_server_received(ptfhost, data):
 
 
 def get_auditd_config_reload_timestamp(duthost):
-    res = duthost.command("sudo service auditd status | grep 'audisp-tacplus re-initializing configuration'")
+    res = duthost.shell("sudo journalctl -u auditd --boot | grep 'audisp-tacplus re-initializing configuration'")
     logger.info("aaa config file timestamp {}".format(res["stdout_lines"]))
 
     if len(res["stdout_lines"]) == 0: