Fixed data collection server test error

[iory]

What is this?

The current data collectionn server test waits for data to be saved by waiting for sleep.
In Travis, sometimes the following error occurs.

2022-05-17T16:47:05.2086940Z ##[group]catkin_test_results
2022-05-17T16:47:05.2087101Z + error
2022-05-17T16:47:05.2087176Z + travis_time_end 31
2022-05-17T16:47:05.2087251Z + set +x
2022-05-17T16:47:05.2087549Z Full test results for 'jsk_data/test_results/jsk_data/rosunit-test_data_collection_server.xml'
2022-05-17T16:47:05.2087747Z -------------------------------------------------
2022-05-17T16:47:05.2087917Z <?xml version="1.0" encoding="utf-8"?>
2022-05-17T16:47:05.2088273Z <testsuite errors="0" failures="1" name="unittest.suite.TestSuite" tests="3" time="10.604"><testcase classname="__main__.TestDataCollectionServer" name="test_all" time="4.1161"><failure type="AssertionError">0 not greater than 0
2022-05-17T16:47:05.2088443Z   File "/usr/lib/python3.8/unittest/case.py", line 60, in testPartExecutor
2022-05-17T16:47:05.2088506Z     yield
2022-05-17T16:47:05.2088650Z   File "/usr/lib/python3.8/unittest/case.py", line 676, in run
2022-05-17T16:47:05.2088769Z     self._callTestMethod(testMethod)
2022-05-17T16:47:05.2088929Z   File "/usr/lib/python3.8/unittest/case.py", line 633, in _callTestMethod
2022-05-17T16:47:05.2089042Z     method()
2022-05-17T16:47:05.2089261Z   File "/github/home/ros/ws_jsk_common/src/jsk_common/jsk_data/tests/test_data_collection_server.py", line 93, in test_all
2022-05-17T16:47:05.2089437Z     self.check(save_dir, target='image')
2022-05-17T16:47:05.2089719Z   File "/github/home/ros/ws_jsk_common/src/jsk_common/jsk_data/tests/test_data_collection_server.py", line 35, in check
2022-05-17T16:47:05.2089829Z     self.assertGreater(len(sub_dirs), 0)
2022-05-17T16:47:05.2089987Z   File "/usr/lib/python3.8/unittest/case.py", line 1310, in assertGreater
2022-05-17T16:47:05.2090125Z     self.fail(self._formatMessage(msg, standardMsg))
2022-05-17T16:47:05.2090267Z   File "/usr/lib/python3.8/unittest/case.py", line 753, in fail
2022-05-17T16:47:05.2090388Z     raise self.failureException(msg)
2022-05-17T16:47:05.2090971Z </failure></testcase><testcase classname="__main__.TestDataCollectionServer" name="test_request" time="3.4055" /><testcase classname="__main__.TestDataCollectionServer" name="test_timer" time="3.0820" /><system-out>&lt;![CDATA[
2022-05-17T16:47:05.2090978Z
2022-05-17T16:47:travis05.2091161Z ]]&gt;</system-out><system-err>&lt;![CDATA[
2022-05-17T16:47:05.2091583Z /github/home/ros/ws_jsk_common/src/jsk_common/jsk_data/tests/test_data_collection_server.py:45: YAMLLoadWarning: calling yaml.load() without Loader=... is deprecated, as the default Loader is unsafe. Please read https://msg.pyyaml.org/load for full details.
2022-05-17T16:47:05.2091671Z   data = yaml.load(f)

https://github.com/jsk-ros-pkg/jsk_common/runs/6474853000?check_suite_focus=true

This PR fixes this error.