[travis] extend ncp transport coverage (#4000)
[travis] extend ncp transport coverage (#4000)

This commit makes the travis run scan-build twice, for the UART and
the SPI NCP configurations respectively.
jwhui/openthread,jwhui/openthread,bukepo/openthread,bukepo/openthread,bukepo/openthread,srickardti/openthread,librasungirl/openthread,srickardti/openthread,turon/openthread,chshu/openthread,srickardti/openthread,lanyuwen/openthread,chshu/openthread,bukepo/openthread,turon/openthread,chshu/openthread,chshu/openthread,chshu/openthread,librasungirl/openthread,jwhui/openthread,lanyuwen/openthread,turon/openthread,openthread/openthread,lanyuwen/openthread,lanyuwen/openthread,abtink/openthread,librasungirl/openthread,librasungirl/openthread,srickardti/openthread,lanyuwen/openthread,abtink/openthread,jwhui/openthread,turon/openthread,lanyuwen/openthread,openthread/openthread,openthread/openthread,abtink/openthread,chshu/openthread,openthread/openthread,abtink/openthread