By Vladyslav Smilianets and Leah Millis SOUTHERN REGION OF DONBAS, Ukraine (Reuters) – Squelching through thick mud on Tuesday, Petro, a Ukrainian soldier dug in not far from Russian positions in the Donbas, recounted matter-of-factly how his unit had to use buckets to clear out water-logged trenches. “We’re more or less okay, but it’s bit harder now because of the rain and a light frost. It’s a swamp. It’s dried a bit today…,” the 35-year-old said, warming up in a dugout near the trenches. “It’s okay, we’re holding up,” he added, laughing. Heavy rain and falling temperatures are making cond…