Add tests cases for 1.6.x -> 1.7.2 upgrade

src/box/lua/schema.lua

test/xlog/suite.cfg

test/xlog/upgrade/1.7.2/00000000000000000000.snap

test/xlog/upgrade/1.7.2/00000000000000000000.xlog

test/xlog/upgrade/1.7.2/00000000000000000005.xlog

test/xlog/upgrade/1.7.2/00000000000000000010.xlog

test/xlog/upgrade/1.7.2/00000000000000000015.xlog

test/xlog/upgrade/1.7.2/00000000000000000020.xlog

test/xlog/upgrade/1.7.2/00000000000000000025.xlog

test/xlog/upgrade/1.7.2/00000000000000000030.xlog

test/xlog/upgrade/1.7.2/00000000000000000031.xlog

test/xlog/upgrade/1.7.2/version