HDF5 file access rights

[7schroet]

Some of the HDF5-related functions request more rights than necessary in sections that only read the state. This PR adjusts the rights in the corresponding H5Fopen function calls.

While it is not fundamentally wrong to request RDWR access here, HDF5 applies a file lock in this case, which can lead to errors if multiple of the cloudsc prototypes are run simultaneously, for example in a benchmark setting. The lock-induced errors look like this:

[...]
HDF5-DIAG: Error detected in HDF5 (1.14.3) thread 0:
  #000: [...]/src/H5F.c line 836 in H5Fopen(): unable to synchronously open file
    major: File accessibility
    minor: Unable to open file
[...]

Note that file locking can also be disabled altogether by setting the environment variable HDF5_USE_FILE_LOCKING=FALSE, but users might not be aware of this option.

The changes were tested locally, without any trouble.

[FussyDuck]

All committers have signed the CLA.

[MichaelSt98]

Thanks for this contribution!
I have no objections and it makes sense to open in RDONLY mode.

@7schroet could you please sign the CLA?
Once the CLA is signed and the checks have passed I'll approve and we can merge this.

[MichaelSt98]

Clean addition/fix.
Ready to be merged once CLA is signed.

[7schroet]

Thanks for the quick feedback, the CLA is now signed!

[reuterbal]

Many thanks for this!