Clean up info printing at CDS dump time

A small clean up of a couple of small issues when printing out information during CDS dump time:

1. The "Unknown" type of metadata is no longer needed -- after JDK-8072061 (Automatically determine optimal sizes for the CDS regions) we know the exact type of every metadata block in the CDS archive.

2. The following size output needs to be indented properly to accommodate 2- and 3-letter names in the first column.

mc space: 21736 [ 0.1% of total] out of 24576 bytes [ 88.4% used] at 0x0000000800000000
rw space: 4229896 [ 23.4% of total] out of 4231168 bytes [100.0% used] at 0x0000000800006000
ro space: 7227952 [ 40.0% of total] out of 7229440 bytes [100.0% used] at 0x000000080040f000
md space: 6064 [ 0.0% of total] out of 8192 bytes [ 74.0% used] at 0x0000000800af4000
od space: 6404560 [ 35.4% of total] out of 6406144 bytes [100.0% used] at 0x0000000800af6000
st0 space: 102400 [ 0.6% of total] out of 102400 bytes [100% used] at 0x00000007bfc00000
oa0 space: 65536 [ 0.4% of total] out of 65536 bytes [100% used] at 0x00000007bf800000
total : 18058144 [100.0% of total] out of 18067456 bytes [ 99.9% used]