Fix minor spelling mistakes

Trivial spelling mistake fix in error message text.

• Fix spelling mistake "adminstrator" -> "administrator"
• Fix spelling mistake "specificed" -> "specified"
• Fix spelling mistake "interperted" -> "interpreted"

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #4728