fix(method): local variable 'pkg_path' referenced before assignment
fix(method): local variable 'pkg_path' referenced before assignment

sct failed in test-provision phase with error:
Traceback (most recent call last):
File "/sct/sdcm/tester.py", line 127, in wrapper
return method(*args, **kwargs)
File "/sct/sdcm/utils/common.py", line 153, in inner
res = func(*args, **kwargs)
File "/sct/sdcm/tester.py", line 280, in setUp
node.install_manager_agent(mgmt_auth_token, repo, package_path=pkg_path)

problem that 'scylla_mgmt_pkg' config parameter  is not configured. in this case the pkg_path
is not initialized before using

scylladb/scylla-longevity-tests,scylladb/scylla-cluster-tests,scylladb/scylla-cluster-tests,scylladb/scylla-cluster-tests,scylladb/scylla-cluster-tests,scylladb/scylla-longevity-tests,scylladb/scylla-longevity-tests,scylladb/scylla-cluster-tests