erasure-code: define the ErasureCodeProfile type

erasure-code: define the ErasureCodeProfile type

Instead of map<string,string>. Make it a non const when initializing
an ErasureCodeInterface instance so that it can be modified.

Rename parameters into profile for consistency with the user
documentation. The parameters name was chosen before the user interface
was defined. This cosmetic update is made in the context of larger
functional changes to improve error reporting and user interface
consistency.

The init() method are made to accept non const parameters.  It is
desirable for them to be able to modify the profile so that is
accurately reflects the values that are used. The caller may use this
information for better error reporting.

Signed-off-by: Loic Dachary <ldachary@redhat.com>