Parent directory in the explorer does not support all path formats

In HDFS-15239, a new button can click to parent folder is add. However, if the path is not formatted perfectly, it will not get the real parent.

Path like follows are supported to get the file list in explorer.html, but they do not get the correct parent:

/a/b/c/ parent will get  /a/b/c now which should be /a/b

/a/b//c parent's parent will get /a/b now which should be /a

Otherwise, if current path is / or // or ///..... The parent button should be unabled as it has no parent.