Fix various issues/warnings that come up on Jenkins (#7147)

* Avoid warning about swap being unlimited

Currently we get the following message on Jenkins:
"Your kernel does not support swap limit capabilities or the cgroup is not mounted. Memory limited without swap."

Since we're not limiting swap anyway, we might as well avoid trying to.
https://docs.docker.com/config/containers/resource_constraints/#--memory-swap-details

* Fix escaping in re.search()

* Fix escaping in _noisy_layer()

* Raise a more descriptive error when dashboard data isn't found

* Don't error on dashboard files not being found when webui isn't required

* Change dashboard error to a warning instead

python/ray/dashboard/dashboard.py

@@ -8,6 +8,7 @@ except ImportError:
 import argparse
 import copy
 import datetime
+import errno
 import json
 import logging
 import os
@@ -323,12 +324,13 @@ class Dashboard(object):
         build_dir = os.path.join(
             os.path.dirname(os.path.abspath(__file__)), "client/build")
         if not os.path.isdir(build_dir):
-            raise ValueError(
-                "Dashboard build directory not found at '{}'. If installing "
+            raise OSError(
+                errno.ENOENT,
+                "Dashboard build directory not found. If installing "
                 "from source, please follow the additional steps required to "
-                "build the dashboard: "
-                "cd python/ray/dashboard/client && npm ci && npm run build"
-                .format(build_dir))
+                "build the dashboard "
+                "(cd python/ray/dashboard/client && npm ci && npm run build)",
+                build_dir)
 
         static_dir = os.path.join(build_dir, "static")
         self.app.router.add_static("/static", static_dir)
@@ -925,4 +927,7 @@ if __name__ == "__main__":
                    "error:\n{}".format(os.uname()[1], traceback_str))
         ray.utils.push_error_to_driver_through_redis(
             redis_client, ray_constants.DASHBOARD_DIED_ERROR, message)
-        raise e
+        if isinstance(e, OSError) and e.errno == errno.ENOENT:
+            logger.warning(message)
+        else:
+            raise e