Dtests failing intermittently on Jolokia agent

Error Message
subprocess.CalledProcessError: Command '('/usr/lib/jvm/java-8-openjdk-amd64/bin/java', '-cp', '/usr/lib/jvm/java-8-openjdk-amd64/lib/tools.jar:/home/cassandra/cassandra/cassandra-dtest/tools/../lib/jolokia-jvm-1.7.1-agent.jar', 'org.jolokia.jvmagent.client.AgentLauncher', '--host', '127.0.0.1', 'start', '706')' returned non-zero exit status 1.
Stacktrace
self = <auth_test.TestAuthRoles object at 0x7fc6cb4313a0>

(...)

    
        mbean = make_mbean('auth', type='RolesCache')
>       with JolokiaAgent(self.cluster.nodelist()[0]) as jmx:

auth_test.py:1888: 
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 
tools/jmxutils.py:309: in __enter__
    self.start()
tools/jmxutils.py:187: in start
    subprocess.check_output(args, stderr=subprocess.STDOUT)
/usr/lib/python3.8/subprocess.py:415: in check_output
    return run(*popenargs, stdout=PIPE, timeout=timeout, check=True,
_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ 

input = None, capture_output = False, timeout = None, check = True
popenargs = (('/usr/lib/jvm/java-8-openjdk-amd64/bin/java', '-cp', '/usr/lib/jvm/java-8-openjdk-amd64/lib/tools.jar:/home/cassandr...t/tools/../lib/jolokia-jvm-1.7.1-agent.jar', 'org.jolokia.jvmagent.client.AgentLauncher', '--host', '127.0.0.1', ...),)
kwargs = {'stderr': -2, 'stdout': -1}
process = <subprocess.Popen object at 0x7fc6c9afb910>
stdout = b"Couldn't start agent for PID 706\nPossible reason could be that port '8778' is already occupied.\nPlease check the standard output of the target process for a detailed error message.\n"
stderr = None, retcode = 1

(...)

            if check and retcode:
>               raise CalledProcessError(retcode, process.args,
                                         output=stdout, stderr=stderr)
E               subprocess.CalledProcessError: Command '('/usr/lib/jvm/java-8-openjdk-amd64/bin/java', '-cp', '/usr/lib/jvm/java-8-openjdk-amd64/lib/tools.jar:/home/cassandra/cassandra/cassandra-dtest/tools/../lib/jolokia-jvm-1.7.1-agent.jar', 'org.jolokia.jvmagent.client.AgentLauncher', '--host', '127.0.0.1', 'start', '706')' returned non-zero exit status 1.

/usr/lib/python3.8/subprocess.py:516: CalledProcessError