Generate package version automatically

[esyr-rh]

Right now, RPM version is more or less arbitrary and has to be provided manually. We can try to generate it during the prepare_source stage based on the information we have:

• Kernel version from which source files are originated
• Version of kernel modules themselves, as provided in MODULE_VERSION directive

I'm tempted to use the first one exclusively, as there is, for example, mpt3sas package, that contains both mpt3sas and mpt2sas kermel modules (which are placed in the same directory) that have different versions, so, unless we enforce "one *.ko per one package" rule, trying to use MODULE_VERSION information could lead to problems.