Add libzutil for libzfs or libzpool consumers

Adds a libzutil for utility functions that are common to libzfs and
libzpool consumers (most of what was in libzfs_import.c).  This
removes the need for utilities to link against both libzpool and
libzfs.

Reviewed-by: Matthew Ahrens <mahrens@delphix.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Don Brady <don.brady@delphix.com>
Closes #8050

include/sys/zfs_context.h

@@ -663,7 +663,6 @@ extern void random_init(void);
 extern void random_fini(void);
 
 struct spa;
-extern void nicenum(uint64_t num, char *buf, size_t);
 extern void show_pool_stats(struct spa *);
 extern int set_global_var(char *arg);
 

include/sys/zfs_ioctl.h

@@ -372,6 +372,7 @@ typedef struct zinject_record {
 #define	ZINJECT_NULL		0x1
 #define	ZINJECT_FLUSH_ARC	0x2
 #define	ZINJECT_UNLOAD_SPA	0x4
+#define	ZINJECT_CALC_RANGE	0x8
 
 #define	ZEVENT_NONE		0x0
 #define	ZEVENT_NONBLOCK		0x1