Given output of dmsetup ls this will return
    themajor:minor (block name) of the device deviceName

def getMajorMinor(deviceName, dmsetupLs):
    """
    Given output of dmsetup ls this will return
    themajor:minor (block name) of the device deviceName
    """

    startingIndex = string.rindex(dmsetupLs, deviceName) + len(deviceName)
    endingIndex = string.index(dmsetupLs[startingIndex:], "\n") + startingIndex
    # trim the preceding tab and ()'s
    newStr = dmsetupLs[startingIndex + 2: endingIndex - 1]
    return newStr