class/base: fixup install_strip
class/base: fixup install_strip

* adapt to *_ELF now being regex instead of simple strings
* don't call file command, but use python magic module
* support build, host and target elf stripping and not just target

sknsean/core,diorcety/oe-lite-core,hundeboll/core,sknsean/core,hundeboll/core,hundeboll/core,hundeboll/core,diorcety/oe-lite-core,sknsean/core,sknsean/core,sknsean/core