Make /bin/df ignore $BLOCKSIZE
Make /bin/df ignore $BLOCKSIZE

When called without any parameter to override the block size, '/bin/df'
uses the $BLOCKSIZE environment variable. That variable may contain
units like K, M, G, etc.

Before this commit, general.sh took the value of $BLOCKSIZE from the
output of 'df' and used it in arithmetic expressions, which broke them
because of the unit suffixes.

This commit adds the higly portable '-k' option to the 'df' invocation
to explicitly set the value of block size to 1024.

EOSIO/eos,EOSIO/eos,EOSIO/eos,EOSIO/eos,EOSIO/eos