Fifth release candidate for prplMesh v1.5 See https://confluence.prplfoundation.org/display/PRPLMESH/Releases for release notes. Changes from rc4: * ci: add more wireless backhaul tests * Update easymesh_cert_version: Google Sheet fixes * update alpine builder and remove python2 dependency * PPM-960 nl80211: implement set_channel * nl80211: add a space in update command * tlvf: support python2 build for ugw platform * tlvf: support python2 build for rdkb platform * ci: apply UCI settings for scheduled certification tests