KRAMATORSK, Ukraine, April 15 (Reuters) - Ukrainian airborne troops landed in a town in the east of the country on Tuesday apparently at the start of a crackdown to root out pro-Russian separatists - but they pulled back into base after meeting a hostile reception from local civilians. The town of Kramatorsk is one of 10 localities in Ukraine's Russian-speaking east where separatist rebellions have broken out. The move suggested Ukraine's authorities were going ahead with a plan for a broad military crackdown to end the unrest which began 10 days ago. Separately, the state security service announced a similar...