[io][HDF5File] remove `r+` mode from the valid mode

3 jobs for hdf5_scan_file_lock in 2 minutes and 33 seconds (queued for 1 second)
Status Name Job ID Coverage
  Test Library
passed test:python3.5-stretch-pyqt5 #131409

00:01:13

passed test:python3.7_stretch_pyqt5 #131410

00:01:06

 
  Test Notbooks
passed test:test-tomoscan-tutorials #131411

00:01:20