Run fsck before obtaining minimum filesystem size. (#1162215)

resize2fs -P now requires an e2fsck -f first. The lack of a real minimum
size left us with no useful minInstanceSize and allowed users to attempt
a shrink down to any size, which led to failures.

If we have a currentSize, set filesystem.

(cherry picked from commit 8b7d3ba3723a5cc88c56b6a848aae19f7f6a8b63)
Disable resize operations on filesystems whose current size is unknown.

It is not safe to attempt to resize without knowing the current size
or to attempt to shrink without knowing the true minimum size.

(cherry picked from commit e2e854fbe89790452ddf07e87bbc07908932fc8f)

Related: rhbz#1162215
Fix units for fs min size padding.

(cherry picked from commit f62466ac5798d622ddf852d79c819d3b4f4c5db5)
New method to round a Size to a whole number of a specified unit.

(cherry picked from commit 8d9cbb78122e4a2a223a5e6a3f7239715ddb498a)
Round filesystem target size to whole resize tool units. (#1163410)

Add a check in case the rounding changes the direction of resize.

(cherry picked from commit 008e1f58426a634e883095fc5053834fd8768b32)